Thermal wire stripper



Aug. 4, 1964 JQ R. HOOKER 3,143,635

THERMAL .WIRE STRIPPER' Filed NOV. 13, 1962 Fig. 5

INVENTOR. /4 James R. Hoo/rer la v BYNNHTW United States Patent3,143,635 THERMAL W STRWPER James R. Hooker, 4357 Vetter Place, La Mesa,Calif.. 'Filed Nov. 13, 1962, Ser. No. 237,041

7 Claims. (Cl. 21'9-221) This application is a continuation-in-part ofabandoned application S.N. 133,273 tiled August 22, 1961, by I ames R.Hooker.

This invention relates to a device for stripping insulation from theends of an insulated electric wire, and more particularly, to ahand-manipulated, hand-held, electrically-heated thermal wire stripper.

The removal of insulation from the ends of insulated electric connectingwires in order to prepare the wires for connection to associatedapparatus has long been a troublesome chore. A number of solutions havebeen adopted in the art, the most acceptable one in the present state ofthe art being the so-called thermal wire stripper. The mechanicalstripper which was popular in the prior art when connecting wires wereheavier than they have presently become, can no longer be used when ahigh degree of reliability and ruggedness is demanded of the fabricatedelectronic article. The reason for this is that the trend toward lighterand more compact electronic assemblies has led to lighter and thinnerelectrical conductors. The smallest nick and even a shallow scratch,especially at the end of the insulation sleeve remaining on theconductor drastically increases the susceptibility of the wire tobreakage. In addition, the removal of any strands from a multi-strandconductor is not permissible where the conductor is closely dimensionedto a given current capacity or other electrical or mechanicalcharacteristic. It follows that although the mechanical wire stripper isa useful tool under certain circumstances when carefully used, there arehazards and disadvantages to its use which it is desirable to avoid. l

The present connecting wires in the electrical and electronic arts aregenerally insulated with a plastic material such as rubber, neoprene,nylon, teflon, etc., and these materials can be severed by melting orburning. This feature has been recognized in U.S. Patent 2,978,565 toSullivan issued April 4, 1961, which shows a manual type thermal wirestripper. This type device hasnone of the disadvantages of themechanical stripper, but in the .present state of theart there islacking certain conveniences which it is the purpose of the presentinvention to alleviate.

Manual thermal strippers have thermal elements which perform theinsulation severing process. The thermal velements must be sturdy enoughso that even when heated to red heat, they will not soften and distorteven after -performing the insulation removing lprocess many times. Thisrequirement for strengthnecessitates that the thermal elements be of lowelectrical resistance, that is, less than an ohm with the consequencethat a lowstorage, high amperage source must be utilized for heating theelements. This consideration as well as considerations of safety compelthe use vof a step-down transformer so that the usual power line sourcecan be used.

The step-down transformer for the purpose described must be capable ofdeliveringflS or 20 watts. In the present state of the art as shown byPatent 2,978,565, refer e'nced above, this transformerA is not an`integral part vof the manual ther-mal stripper and there is nolimitation on its 'size and weight. There does not apepar to be atransformer of sufficient compactness and suitable shape in the priorart to be considered for inclusion as an integral element in a unitaryhandle shaped manipulated thermal wire stripper. At the same time, theuse of the separate ltransformer presents a number of disadvantages. Thethermal wire stripper has two stripper elements and in 3,143,635Patented Aug. 4.,k 1964 order to avoid cross currents, arcing, etc., thestep-down transformer must be provided with two separate secondarywindings so that the excitation of each element is independent of theother. This requirement results in the necessity for two pairs of heavyflexible insulated electric cable to be connected to the stripper tool.

These leads are required to carry a current of ten amperes or morewithout appreciable heating or voltage drop. It follows that the leadsmust be of thick conductors and they are heavy and cumbersome andinterfere with the deft manipulation of the stripper. Further, suchleads are expensive, because the need for extreme flexibility requiresthat the leads be cable of many strands of very ine wire.

An additional disadvantage inherent in the use of the separate step-downtransformer is the impracticality of remotely switching it on and offeach time the stripper performs a stripping operation. The result isthat the transformer is left energized continuously thereby wastingelectrical energy and uselessly dissipating the life of the transformer.Still another disadvantage attendant the use of the separate transformeris that the switch must be in the heavy current secondary circuit.

It is a primary purpose of the present invention to provide anelectrically energized thermal wire stripper which avoids theshortcomings of prior art devices.

It is another object of the present invention to provide a lightweighthand-size, handle-shaped thermal wire stripper which contains as anintegral part, its own step-down transformer, and therefore requires forits energization only one light electrical feed cord.

Still another object of the present invention is to provide a step-downtransformer of handle shape and improved eiciency to cooperatestructurally and functionally as yan integral part of a hand held andmanipulated thermal wire stripper.

Another object of the present invention is to provide thermal wirestripper thermal elements of improved eiiiciency to cooperate with asmall eflicient step-down transformer.

Another object is to provide a thermal Wire stripper of improved ease inhandling and improved economy and durability in operation.

Still another object is to provide a thermal wire stripper which iscomfortably carried in one hand and in which manipulation forenergization and stripping are conveniently all accomplished by the samehand.

For a better understanding of my invention together with other andfurther objects thereof, reference is made to the following description,taken in connection with the accompanying drawing made a part of thisspecification, and in which:

FIGURE lis a perspective view of a thermal wire stripper in accordancewith this invention,

FIGURE 2 is a'perspective view of the interior of the housing half casesinexploded relation,

FIGURE 3. is a vertical side view of a complete thermal wire stripper inaccordance with the present invention with one half case removed, andFIGURE 3a is a modiiication thereof.

FIGURE 4 is a toppartly-in-section View of the lower thermal element andits support,

FIGURE 5 is a vertical plan View of a thermal element, and l FIGURE 6 isa schematic diagram of the step-down transformer.

Referring tothe drawing in detail, FIGURE 1 shows the stripper housinglor case -11 to comprisey two half cases 30 and 30. Throughout thisdescription, like parts of half case 3) and half case 30 are indicatedby reference numorals and their primes respectively. yThe half cases arewith few exceptions, mirror images of one another. Case frial. case 30,30 has an elongated flat face 40, 40 respectively of the narrow flange.

,with pin 60'.

' o 11 is of handle shape, that is, a size and shape to be comfortablyand conveniently gripped by a hand, and I have found that an elongatedshape of five inches in length and transverse dimensions of one andone-half inches by one 4and one eighth inches to be suitable formanipulation by the average adult hand. The dimensions may be variedsomewhat to suit smaller hands, if desirable.

In more detail, case 11 comprises a columnar portion A V34, 34' withrounded-edges and a length of about three and three eighthinches, afront truncated pyramidalportion 35, 35 having a length of about one andone eighth inches and a rear truncated pyramidal portion 37, 37 with alength of about one half inch. The terms front and u i rear as usedherein refer to the device as grasped for Vuse with the thumb end asfront. This is also the end from which the thermal stripper elements aresupported.

Case 11 provides the handle for the stripper, the houslator bar 12,anchorage for a single electric supply line 76 and insulationsupports 78and 100 for stripper element supporting stanchions 13, 14 and 15, 16.The stripper thermal elements V17 and 18 are electrically and ing forthe transformer, the socket and support for manipumechanically affixedto the ends of stanchons 13, 14 and u ported on stanchions 15, 16 andcan be locked in any selected position to permit accurate stripping of aselected length of insulation from a plurality of conductors.

AThe assembly of a handle, a lower fixed pair of stanchions and stripperelement, and a pivoted upper pair of stanchions with its stripperelement resembles and is aptly described as a jaw or mandiblearrangement.

The case 11 is constructed of any strong thin material such as sheetmetal or high impact strength plastic mate- Referring to FIGURE 2, it isseen that each half sol and two inwardly converging faces 42, 44, and42', 44 s ,flange 46 extending from the front end of the case half tothe rear end of flat face 40 and at right angles to flat v.face 40. Awide fiange 48 having a width equaluto` half the case thickness extendsfrom the front end of the case to and around the rear end of the case tothe front edge of the rear truncated portion Where it joins the rear endHalf casef has similar flanges 46 and 48'.l Attached to the insidesurface of the narrow flange are depending tabs 50, 52 and 5W, 52 whichact as channels for the power supply line directed to and from V,theswitch Vassociated with, switch button 19 at the front end of thedevice. The rear face of Wide flanges 48, 48,

Vare provided with a rectangular cut-outto anchor a rubbersubstantially, and being affixed to flat face proximately at the rearend `near the Vwide flange thereof. A second.

element 58 of elongated cylindrical shape and having an internallyAthreaded free end serves as a pivot pin for manipulator bar 12, as wellas the nut for a small bolt for securing the case halves together. Aferrule 58 in case half 30 cooperates' with pivot pin 58 to support pin58 and alsoto secure the case halves together.

A third anchor pin 60' is aixed to the front end of half case L30 alongthe median line thereof and at a point one-third the length of thetruncated face 42 from the line ofjuncture with fiat face 40.Interiorly. of the front end of halfV case 30 is a short ferrule 60located to cooperate Also provided lin case half 30 is a ferrule (notshown) corresponding to ferrule 56 in case half 30.

Half-case 30' is the mirror image of half case 30 with 4the exceptionofthe anchor and pivot pinsas described above and two other elements.Only case half 30 is prod. former in place.

wide flange 48 a distance equal to the cross-sectiona1 height oftransformer core 75. These brackets hold transformer 7 4 firmly in placein case lll.

The mechanical cooperation between the various elei land compactness. Itmust be capable, in spite of its small size, of energizing the thermalelements without becoming uncomfortably warm to the hand. The heat ofcontinuous magnetization current is avoided by the provision of a switchin its primary circuit so that it is energized only when severing theinsulation during a stripping operation. Even so, it is necessary thatthis transformer be of unique efficiency and capacity to fulfill itsfunction in spite of its compactness. In this respect the thermalelements are also of unique shape to cooperate with the transformer byminimizing the power demand to a value compatible with the ability ofthe transformer.

The core 75 of transformer 74 is limited in size by the necessity for acomfortable manipulative size of the case 11. The dimensions of the caserestrict the cross section of the transformer core to no greater thanone and onequarter square inches. I have found that the usualtransformer irons, such as A.I.S.I. types M-l4 to M-l9 are not capableof the required performance. These irons demand a prohibitively highmagnetization current. In fact, with the usual transformer iron themagnetization current alone causes this smallcore to operate close to`saturation and the generation of heat in the core is excessive. I havefound that a core of the diminuative size required meets therequirements capably if made of grain oriented silicon steel A.I.S.I.type M-6. This steel has a saturation level of 14,000 gausses and in thetransformer Vo-f the construction shown, requires only milliamperesAconfiguration and 0.0143 inch thick, approximately.

Each lamination has two winding windows each having a width of 0.225inch and a height of 0.60 inch approximately. As mentioned above, thetransformer primary 87 is energized by power cable '76 through a switchcontrolled by button 19. e

Transformer 74 is provided with two secondary windings 88 and 88 asshown in FIGURE 6. Secondary 88 has two terminals which exit from thewinding 84 on opposite sides thereof. Thus terminal 90 is connected tothermal element stanchion 16 and terminal 92 shown in FIGURE 6 buthidden in FIGURE 3 by the transformer winding is connected to stanchion15. Terminals 90 and 92' of secondary 88 are likewise connected tostanchions 14 and 13 respectively. The connections to stanchion's 13 and14, are of flat flexible preferably resilient laminations to permitready fiexure as upper jaw is operated during a stripping operation.

Referring to FIGURES l and 3, itis seen that stanchions 15 and 16 arestationary relative to case l11. These stanchions provide bothelectrical connection to and mechanical support for thermal element -18.Insulation block 78 provides a rigid mechanical support for stanchions15 and 16. It follows that insulation block 78 itself must be rigidlyaffixed with respect to case 11. To Y Arms 70 and 72 are spaced apartthe i length of core 75 (see FIG. 3) of transformer 74. Flanges.y 66 and68 are colinear with one another and spaced from the rend that block 78will be rigidly supported and providestrong support for stanchions and16, it is of strong `insulation material such as cloth reenforcedphenolic condensate. It is roughly of truncated triangular shape inoutline in its longitudinal section. Its base portion contains anarcuate relief to provide an arcuate saddle 80 for structural supportwith the end 82 of transformer winding 84. A rectangular relief or slot86 is provided to enable connections to be made to the inner ends ofstanchions 15 and 16.

Block 78 by virtue of saddle 80 is mechanically coupled tightly totransformer 74 so that the length of the connections from thetransformer secondary to the ther- ,mal element stanchions is a minimumand the voltage drop during use is negligible. In order to achieve theseconditions, the transformer secondary terminals are located adjacent thecorresponding stanchion to which connection will be made. In addition,arcuate saddle 80 engages transformer winding end 82 to prevent anyrelative motion between the two, with the result that block 78 is unableto work with respect to the transformer.

FIGURE 4 shows that the outer or narrow end of block 78 is provided withtwo parallel sockets 94 which penetrate from the front surface to slot86. These sockets have a diameter such that threaded end portions 96 of'cylindrical stanchions 15, 16 have a tight screw t therein. Othermechanical couplings between the block 78 and the stanchions arepermissible provided the fit is suilicie'ntly secure to insure againstmovement of the stanchions relative to block 78 even under conditions ofabuse such as dropping.- The jumper conductor 93 composed of a pluralityof ribbon-like conductors of copper v.61. The saddle 80 of block 78engages the end 82 of transformer 74 to provide resistance againstpivoting of block 78 and to prevent relative motion between block 78andthe transformer in order to avoid Working and fatigue of the jumperconnections. In addition faces 103 and 104 of block 78 bear againstflanges 35, 35 and 48, 48 of housing 11.

Transformer 74 core 7S fits snugly between flanges 30, of the case 11and right angle brackets 62, 64 (see FIGURES 2 and 3). The transformerthus supported, has its arcuate end 82 in proximity to establish mutualsupport with insulation block 78 and provide short electricalconnections as aforesaid.

n The provision of a movable mandible-type thermal stripper elementrelative to the lixed element requires a movable insulated support forthe moving element. To this end an insulation block 100 is aixed to thefree end of manipulation bar 12. Manipulation bar 12 is provided with aloop portion at the posterior or back end to provide a socket 102 forengaging hinge pin 58 (FIG- URE 3). The manipulation bar 12 is lof anystrong material and as shown, may be of metal channel crosssectionalshape. It has a width such that it can move freely between the inneredges of flanges 46, 46 of hous-y ing 11 when the half cases 30, 30 arejoined. The manipulation bar V12 manipulation part proper is a littlelonger than the transformer core. The forward end is provided with meansfor rigidly securing to it for motion therewith insulation block 100.Insulation block` insulation blocks are so supported as to form a fixedjaw and a movable jaw in biting relation.

Block has a pair of sockets located similarly to the sockets in block78, for the support of stripper element stanchions 13 and 14. Thesockets are so arranged that with respect to the plane of rotation ofmanipulation bar 12, stanchions 13 and 15 lie inone plane parallel tothe plane of rotation and 16 and 18 lie in a second plane of rotationparallel'to but spaced a selected distance away from the plane ofrotation of stanchions 13 and 15.

A leaf spring having a semi-elliptic leg 106 and a at leg 107 isprovided to urge the movable stripper element away from the fixedelement. Flat leg 107 rests directly upon transformer core 75 whereinproper positioning and support for spring 105 is obtained. Semiellipticleg 106 rests in the channel of manipulator bar 12.

Stripper thermal elements 17 and 18 are shown in detail in FIGURE 5 andare required to have efficient electrical and thermal characteristics asWell as strong mechanical properties. In addition these elements musthave negligible corrosion susceptibility. The desired electrical andthermal characteristics are obtained by a proper reduction in crosssection of the element in the working zone and by a T-shaped reliefsymmetrically positioned to provide thermal isolation of the Workingzone. The element is seen to have a pair of opposed similar re-entrantportions. The working zone is indicated by numeral 109. The element isprovided with spaced tab portions 112 and 113, each provided with acentrally located aperture 114 and 115, respectively for attachingscrews or the like. The tab portions are integrally connected to theworking zone portion 109 by reduced vertical legs 117 and 118, andhorizontal portions 119 and 121. A V-sllaped relief 110 and an arcuaterelief 111 are provided in the working zone portion. The V-shaped reliefperforms two functions; it provides suflicient heat coupling with theinsulated wire to be stripped to sever the insulation, and it localizesmost of the heat generation in the working zone. The V-shaped or othershape such as semi-circular-shaped relief is limited in size somewhat bythe smallest diameter insulated wire to be stripped in the case ofdirectly abutting elements such as shown in FIGURE 3. It is sometimesdesirable, where the depth of the relief in the Working surface is toolimited by the size of the wire to be stripped to give the desired heatconcentration, to provide for additional concentration of resistance inthe working zone by providing additional relief such as shown by 111 inthe nether surface of the elements. An increased adaptability to a widerange of wire sizes is obtained by the over-bite or overlap arrangementshown in FIGURE 3a` inasmuch as deeper V-shaped recesses can be providedto together form an adjustable diamond-shaped orifice to engage the wireto be stripped.

The concentration of resistance in the working zone results in reducingthe demand for electrical energy to only that required for heating theactual working zone. In addition, rapid heating is obtained thusreducing the transfer of heat to non-working and reducing waiting andlost time in the use of the device. The foregoing described congurationof the thermal elements permits the use of a transformer of lower powercapacity than would be required with the thermal elements of the priorart.

The stripper thermal elements are composed of an alloy chosen to havethe characteristic above stated. The `constituent metals are cobalt 0.5to 2.5%, chromium 20.5 to 25%, molybdenum 8 to 10%, tungsten 0.20 to1.0%, iron 17.0 to 20%, carbon 0.05 to 0.15%, silicon not exceeding1.0%, manganese not exceeding 1.0%, and the balance nickel. Thismaterial has excellent oxidation resistance to 2200 degrees F.

The transformer windings for the dimensional embodiment given supra areas follows: Primary winding- 440 turns of No. 28, secondarywindings-each 4 turns of No. 14.

D An operating example of a stripper element has the followingdimensions:

' Inches Total height 0.312 Thickness 0.032 Total width 0.563 Width andheight of tabs 112 and 113 0.186 Length portions 117 and 118 0.054 Widthof side legs 117 and 118 0.062

Radius Vof relief 111 and length of arc 0.500 and 0.2

Manipulator bar 12 is limited in the extent of opening by member 112.This member is anchored in any convenient manner in fixed jaw '7S and isaccommodated by lslot 101 in jaw 100. Member 112 is provided at its freeVtactor 95 against the tension of spring 97 into contact with contacts108l to bridge them. One of contacts 10S is connected to one ofconductors 76 and the other of contacts 108 connects to one terminal oftransformer primary 87. The other conductor of supply line 76 connectsdirectly to the other terminal of transformer primary S7. In operation,the manipulator bar 12 is compressed to cause the thermal elements topress against the insulation to be severed, switch 19 is pressed inwardto energize the transformer and heat the thermal elements. When theinsulation is severed, switch button 19 is released while bar 12 remainssqueezed down to pull the severed insulation off of the conductor beingprepared. It is, therefore, seen that the transformer need be energizedonly for the severing operation and that this is a very brief period,resulting in maximum efficient use of electrical energy and a minimumdemand on the transformer. An additional advantage of this system isthat the stripping elements are not continuously heated during thestripping operation with the result that the cool elements cleaner stripthe severed insulation sleeve off the wire and avoid the generation ofexcess molten debris. Furthermore, the fumes generated by heating someplastic materials to a melting or higher temperature are irritating andeven to some extent, toxic, and the present device keeps the generationof such fumes to an absolute minimum.

This invention has been described with reference to a preferredembodiment, but it is apparent that there may be numerous equivalents ofthe specific details given which may be in accordance with the spirit ofthis invention;

accordingly, it is desired that it be understood that this invention isto be considered limited only by the appended claims taken in the lightof the prior art,

What is claimed is:

1. A manually held thermal wire stripper comprising in combination afixed jaw and a movable jaw each having a thermal stripper member on theworking end thereof, a hollow elongated case of channel cross sectionalshape and hand gripping size and having a uniform cross section middleportion and truncated front and rear ends, an electrical transformersupported in said case middle portion and having primary and first andsecond secondary windings, said fixed jaw comprising a dielectric blockhaving a front portion and a rear portion, said front portion having anintermediate part inwardly inclined and an end part at right angles withrespect to the fore and aft direction thereof, a pair of co-extensiveparallel elongated conductive stanchions spacedly supported at one endin the front right angle part of said dielectric block, means fxedlysupporting said dielectric block in the front truncated portion of saidcase with the fore and aft direction of the block aligned with thedirection of elongation of the case vand with the rear end of thedielectric block abutting the adjacent end of the transformer; aresistance plate member electrically connected to and affixed inbridging transverse relation to the `working end of the stanchions; saidmovable jaw comprising an elongated movable manipulator bar, a pair ofmoving conductive stanchions and a movable resistance plate member, saidmanipulator bar having a middle portion and front and rear end portionsand having an overall length equal approximately to the length of thetransformer plus-the length of the fixed jaw dielectric block in-thedirection of elongation of the case, means pivotably supporting the rearend of the manipulator bar in the rear end p0rtion of the case with anelongated portion of said manipulator bar positionedwithin the open sideof the case in close proximity to the adjacent case walls and extendingoutwardly of said case along the length thereof, said ,manipulator barfront end portion having an intermediate part inwardly inclined withrespect to the manipulator bar middle portion, and an end part at aright angle to the manipulator bar middle portion, means anchoring oneend of each of said movable stanchions in the end part of themanipulator bar front end portion, means supported on said transformerfor resiliently biassing said manipulator bar away from the transformerin said case, and limit stop-means limiting the outward travel of themanipulator bar, means electrically connecting and mechanically affixingsaid movable resistance plate member to the working end of the movablestanchion; an Velectrical pushV button switch, means iixedly supportingsaid switch on the inner surface of the manipulator bar front endportion inwardly inclined part with the push button thereof extendingthrough and outwardly of the manipulator bar; said transformer primarywinding being connected in electrical series with said switch and apower connect'mg cable, means electrically connecting the terminal endsof one of the secondary windings to the fixed ends of the fixed jawstanchions, and exible electrical connecting means connecting theterminal ends of the other secondary winding to the manipulator bar endof the said movable stanchions, whereby the thermal wire stripper isadapted to be powered directly from standard alternating currentsources, and said manipulator bar is adapted to be manually urgedinwardly by the palm of the hand to engage said resistance plates withinsulation to be severed and said push button is adapted to be operatedby the thumb of the same hand to energize said transformer to heat theresistance plate members only so long as is necessary to complete astripping process.

2. The device of claim 1 in which each resistance plate member has aworking portion and a working edge, and is a rigid metal plate ofgenerally rectangular external configuration, said resistance platemember having a T-shaped section symmetrically removed therefrom andcompletely severing the plate portion opposite the working portion toprovide a pair of separated mounting tabs, the working portion of theplate member having a wire insulation receiving notch in the centralportion thereof, and being further progressively reduced in crosssection toward the center thereof by an arcuate relief convex toward theworking edge thereof, whereby the electric power demand for adequateheating of the resistance plate member is minimized by the concentratedutilization of energy in a confined working zone area to thereby permitthe effective utilization of the contained transformer and whereby thestrength and rigidity of the r-,esistance .plate is at the same timemaximized.

3. A hand-held thermal wire stripper comprising in combination,

(a) an upper andV a lower electrically conductive jaw member each havingan anchored end anda working end,

(b) an elongated housing of channel cross sectionalV shape having afront portion, a middle portion and a rear portion, said front portionbeing truncated and hand grip wall members extending adjacent to andpartially enclosing said jaw members,

(c) a resistance plate member having a working zone for severinginsulation and having concentrated electrical resistance in the workingzone, attached to the working end of each jaw member,

(d) first insulation block means having a length substantially equal tothe length of the housing truncated front portion, means iixedlyattaching the anchored end of the lower jaw member to said in sulationblock means, means ixedly supporting said insulation block means in thehousing truncated front portion,

(e) an elongated manipulator bar of dielectric material, means pivotablysupporting one end of the manipulator bar in said housing open sideproximate the rear end thereof, said manipulator bar having a handmanipulating portion equal substantially to the length of the housingmiddle portion and having a lower elongated portion thereof confinedwithin the adjacent walls of the housing to prevent lateral movementthereof and an upper elongated portion extending outwardly of saidhousing along the length thereof and a front portion adjacent the casefront truncated portion extending inwardly; means fixedly attaching theanchored end of the upper jaw member to said manipulator bar inwardlyextending portion whereby said upper jaw member is movably supported formotion in a xed plane toward and away from the xed lower jaw,

(f) an elongated electrical transformer supported in the housing in theuniform cross section portion, said transformer having a magnetic core,a primary winding adapted to be connected to a power source, and twosecondary windings, means electrically connecting one of said secondarywindings in series with the lower jaw resistance plate member,v andmeans for flexibly electrically connecting the other of said secondarywindings to the movable jaw resistance plate member,

(g) resilient biassing means supported on said transformer magnetic coreto support said transformer against movement in said housing and to urgesaid manipulator bar outwardly along the housing.

4. The device of claim 3 in which said transformer secondary windingshave terminals at the same end of the transformer, said transformerbeing supported in the housing with said terminals proximate theanchored ends of said jaws and the electrically connecting meansconnecting the terminals of the secondary windings to the respective jawmembers are heavy iiexible electrical conductors of minimal length.

5. The device of claim 4, wherein the rst insulation block means has afront end extending out of the truncated front portion of the housingand a rear end iixedly supported in the truncated portion of saidhousing against said transformer core, a slot in said insulation blockmeans transverse to the direction of elongation of the housing, a pairof spaced sockets extending from the front end of the insulation blockmeans to the slot and lying in a plane transverse to the direction ofmanipulation of the upper jaw, said lower electrically conductive jawmember comprising a pair of rigid metal rods anchored at one end in saidsockets, means electrically and mechanically attaching said heavyflexible electrical conductors to the metal rods in said transverseslot, said insulation block means being provided with an aperturetransverse with respect to said sockets in the portion rearward of saidslot, securing means passing transversely through the lateral walls ofsaid housing and said insulation block aperture to fixedly secure saidlower jaw and said transformer in and to said housing.

6. The device of claim 5 wherein the manipulator bar front inwardlyinclined portion is provided with a switch button receiving aperturepassing transversely therethrough, a push button electrical switch,means iixedly attaching said switch to the inside surface of themanipulator bar inwardly inclined portion with the switch push buttonextending outwardly of said manipulator bar through said aperture,electrical connecting means electrically connecting said switch inelectrical series connection with the transformer primary winding andpower supply connecting means, whereby said thermal wire stripper jawsare manipulated by the palm of the hand and the thermal resistance platemembers are electrically heated at will by thumb manipulation of theswitch button.

7. An insulation stripper element for a thermal wire stripper comprisinga metallic resistance plate member of generally rectangular shape havinga working edge, a generally T-shaped slot symmetrically located in saidresistance plate member with the end of the stem of the T extendingthrough the edge of the resistance plate member opposite the workingedge thereby providing adjacent isolated terminal tab members in saidresistance plate member, said resistance plate member working edge beingprovided with a wire receiving notch in the middle thereof, the cross ofthe T-slot extending parallel to the working edge of the resistanceplate member, and the portion of the resistance plate member adjacentthe upper edge of the cross of the T-slot having a centrally locatedarcuate relief, convex toward the working edge to concentrate theresistance of the resistance plate member in the middle portion of theworking edge to thereby concentrate the generation of electrical heatingin the middle portion while preserving the rigidity and strength of theresistance plate member to prevent distortion thereof as a result ofstripping operations.

References Cited in the file of this patent UNITED STATES PATENTS1,595,799 Massingham Aug. 10, 1926 2,192,056 Watts Feb. 27, 19402,709,743 Mitchell May 31, 1955 2,745,939 Lenk May 15, 1956 2,768,276Arntzen Oct. 23, 1956 2,978,565 Sullivan et al. Apr. 4, 1961 UNITED".vkSTATES PATENT OFFICE CERTIFICATE OF CORRECTION; Patent No. 3,143,635August 4, 1964 g James Ra Hooker It is hereby certifiedl that errorappears in the above numbered patient4 requiring correction and that thesaid Letters Patent should read as corrected below.,

Column I, line 56, for' nstorage" read voltage line 66, for "apepar".read appear Signed and sealed this 5th day of January 1965.

Att-esta; ERNEST We. SWIDER' EDWARD J. BRENNER` Attesting OfficerCommissionerof Patents UNITED STATES PATENT GEEICE CERTIFICATE 0FCORRECTION August 4, 1964 Patent No. 3,143,635

James Ro Hooker in the above numbered pat#- that error appears tersPatent should read as It is hereby certified t the said Let ent.requiring correction and the,

Column l, line 56, for "storage" re line 66xl for "apepar" read appearSigned and sealed this 5th day of January 1965.

(SE-ALJ Attest:

EDWARD J BRENNER.

ERNEST W. SWIDER Attesting Officer Commissioner. of Patents

3. A HAND-HELD THERMAL WIRE STRIPPER COMPRISING IN COMBINATION, (A) ANUPPER AND A LOWER ELECTRICALLY CONDUCTIVE JAW MEMBER EACH HAVING ANANCHORED END AND A WORKING END, (B) AN ELONGATED HOUSING OF CHANNELCROSS SECTIONAL SHAPE HAVING A FRONT PORTION, A MIDDLE PORTION AND AREAR PORTION, SAID FRONT PORTION BEING TRUNCATED AND HAND GRIP WALLMEMBERS EXTENDING ADJACENT TO AND PARTIALLY ENCLOSING SAID JAW MEMBERS,(C) A RESISTANCE PLATE MEMBER HAVING A WORKING ZONE FOR SEVERINGINSULATION AND HAVING CONCENTRATED ELECTRICAL RESISTANCE IN THE WORKINGZONE, ATTACHED TO THE WORKING END OF EACH JAW MEMBER, (D) FIRSTINSULATION BLOCK MEANS HAVING A LENGTH SUBSTANTIALLY EQUAL TO THE LENGTHOF THE HOUSING TRUNCATED FRONT PORTION, MEANS FIXEDLY ATTACHING THEANCHORED END OF THE LOWER JAW MEMBER TO SAID INSULATION BLOCK MEANS,MEANS FIXEDLY SUPPORTING SAID INSULATION BLOCK MEANS IN THE HOUSINGTRUNCATED FRONT PORTION, (E) AN ELONGATED MANIPULATOR BAR OF DIELECTRICMATERIAL, MEANS PIVOTABLY SUPPORTING ONE END OF THE MANIPULATOR BAR INSAID HOUSING OPEN SIDE PROXIMATE THE REAR END THEREOF, SAID MANIPULATORBAR HAVING A HAND MANIPULATING PORTION EQUAL SUBSTANTIALLY TO THE LENGTHOF THE HOUSING MIDDLE PORTION AND HAVING A LOWER ELONGATED PORTIONTHEREOF CONFINED WITHIN THE ADJACENT WALLS OF THE HOUSING TO PREVENTLATERAL MOVEMENT THEREOF AND AN UPPER ELONGATED PORTION EXTENDINGOUTWARDLY OF SAID HOUSING ALONG THE LENGTH THEREOF AND A FRONT PORTIONADJACENT THE CASE FRONT RUNCATED PORTION EXTENDING INWARDLY; MEANSFIXEDLY ATTACHING THE ANCHORED END OF THE UPPER JAW MEMBER TO SAIDMANIPULATOR BAR INWARDLY EXTENDING PORTION WHEREBY SAID UPPER JAW MEMBERIS MOVABLY SUPPORTED FOR MOTION IN A FIXED PLANE TOWARD AND AWAY FROMTHE FIXED LOWER JAW, (F) AN ELONGATED ELECTRICAL TRANSFORMER SUPPORTEDIN THE HOUSING IN THE UNIFORM CROSS SECTION PORTION, SAID TRANSFORMERHAVING A MAGNETIC CORE, A PRIMARY WINDING ADAPTED TO BE CONNECTED TO APOWER SOURCE, AND TWO SECONDARY WINDINGS, MEANS ELECTRICALLY CONNECTINGONE OF SAID SECONDARY WINDINGS IN SERIES WITH THE LOWER JAW RESISTANCEPLATE MEMBER, AND MEANS FOR FLEXIBLY ELECTRICALLY CONNECTING THE OTHEROF SAID SECONDARY WINDINGS TO THE MOVABLE JAW RESISTANCE PLATE MEMBER,(G) RESILIENT BIASSING MEANS SUPPORTED ON SAID TRANSFORMER MAGNETIC CORETO SUPPORT SAID TRANSFORMER AGAINST MOVEMENT IN SAID HOUSING AND TO URGESAID MANIPULATOR BAR OUTWARDLY ALONG THE HOUSING.